Chapter 12 The rock coast of Japan by T. Sunamura, H. Tsujimoto, and H. Aoki Geological Society, London, Memoirs Volume 40(1):203-223 July 25, 2014 © The Authors 2014

(a) Tectonic setting of the Japanese islands. (a) Tectonic setting of the Japanese islands. (b) Relative sea-level height at 6000 a BP (Nakada et al. 1991) indicated by contours in metres above present mean sea level (MSL) and three typical sea-level curves since mid-Holocene selected respectively at Sado, Muroto and Sendai (Nakada et al. 1991) shown in the insets; and elevation (metres above MSL) of palaeoshoreline of mid-Holocene (Ota et al. 2010) depicted by bold numerals. T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

(a) Three types of rocky coasts. (a) Three types of rocky coasts. (b) Lithological map of Japan (modified from Kojima 1980) and nationwide distribution of rocky coast types. T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

Demarcation diagram of rocky coasts in microtidal environments: type A platforms for ρgHl/Sc≥1.3×10−2, type B platforms for 1.7×10−3≤ ρgHl /Sc <1.3×10−2, and plunging cliffs for ρgHl/Sc<1.7×10−3, where Hl is the largest height of waves occurring at a coast, Sc is the compressive strength of rocks forming the coast, ρ is the density of water, and g is the acceleration owing to gravity (Sunamura 1992). Demarcation diagram of rocky coasts in microtidal environments: type A platforms for ρgHl/Sc≥1.3×10−2, type B platforms for 1.7×10−3≤ ρgHl /Sc <1.3×10−2, and plunging cliffs for ρgHl/Sc<1.7×10−3, where Hl is the largest height of waves occurring at a coast, Sc is the compressive strength of rocks forming the coast, ρ is the density of water, and g is the acceleration owing to gravity (Sunamura 1992). Reproduced by permission of John Wiley & Sons. T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

(a) Coastal waters around Japan. (a) Coastal waters around Japan. (b) Largest storm waves (significant wave height and period) at 31 measuring stations and distribution of mean spring tidal range. (c) Davies et al.'s (2004) study area of the southwestern coast of the Kii Peninsula. (d) Study site at Ebisu-jima of the Susaki Promontory. T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

Rocky coast evolution models for microtidal environments. Rocky coast evolution models for microtidal environments. (a) Uplift scenario in which three crustal movements with the same uplift amount (within a few metres) occurring at the same interval are written. (b) Model A, a model illustrates evolution occurring under the condition that enables development of type A platforms independent of the initial boundary condition. (c) Model B-1 and (d) model B-2; models are different depending on the initial boundary condition, but both have step-like features indicating uplift evidence. (e) Model C explains evolution with no significant features of uplift. Note that all model diagrams are greatly exaggerated vertically. T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

Six datasets showing notch development in model cliffs owing to breaking waves. Six datasets showing notch development in model cliffs owing to breaking waves. No. 1 taken from Sunamura (1973) and the others from Sunamura (1991). T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

Five datasets showing notch development in model cliffs owing to broken waves (Sunamura 1973). T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

Temporal variation in erosion distance in breaking-wave experiments. T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

Temporal variation in erosion distance in broken-wave experiments. T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

Relationship between cliff erosion rate, dX/dt, and dimensionless quantity including wave and rock factors, ρgHf/Sc. Relationship between cliff erosion rate, dX/dt, and dimensionless quantity including wave and rock factors, ρgHf/Sc. T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

Wave height attenuation on a type B platform. Wave height attenuation on a type B platform. Data from Ogawa et al. (2011, figs 2a & 7b). T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

(a) Dependence of α in equation (17) upon relative water depth, h/He. (a) Dependence of α in equation (17) upon relative water depth, h/He. (b) Dependence of β in equation (17) upon relative water depth, h/He. T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

Relationship between platform width and compressive strength of platform-forming rocks on the southwestern coast of the Kii Peninsula. Relationship between platform width and compressive strength of platform-forming rocks on the southwestern coast of the Kii Peninsula. The curve is a best fit of equation (25) to the data points. T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

Relationship between platform development rate, dX/dt, and compressive strength of platform-forming rocks, Sc, for different times. Relationship between platform development rate, dX/dt, and compressive strength of platform-forming rocks, Sc, for different times. T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

Ebisu-jima platform at the southern tip of the Susaki Promontory. Ebisu-jima platform at the southern tip of the Susaki Promontory. The MEM measuring site is located 1.5 m above the cliff-platform junction. The photograph was taken at low tide. T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

MEM measuring site on the landward cliff composed of tuffaceous sandstone. MEM measuring site on the landward cliff composed of tuffaceous sandstone. The inset shows the modified MEM to facilitate application to a steep slope. T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

Height of storm surge plotted against significant height of waves. Height of storm surge plotted against significant height of waves. JMA's wave and tidal data at Irozaki were used. Waves more than 2 m in height were selected from data during the MEM measurement term of 4.3 years (17 May 2004 to 31 August 2008). T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

Idealized profile of the Ebisu-jima platform and definition sketch. T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014

(a) Temporal variations in actual erosion distance of landward cliff of the Ebisu-jima platform (denoted by the star symbol), and in cumulative erosion distances obtained through model calculation with different K-values (by the dotted and the solid lines). (a) Temporal variations in actual erosion distance of landward cliff of the Ebisu-jima platform (denoted by the star symbol), and in cumulative erosion distances obtained through model calculation with different K-values (by the dotted and the solid lines). Mean rate of actual erosion, indicated by the gradient of a dashed line passing through the origin of the graph. Erosion distance at each storm event (ΔX), which is based on the cumulative distance by the dotted line, is shown in the lower bar chart. (b) Time-series data of significant waves in front of the platform. Wave period is plotted only for waves causing erosion (ΔX>0) for easy reading of the diagram. Roman numerals at the bottom of the diagram denote four MEM measurement terms. T. Sunamura et al. Geological Society, London, Memoirs 2014;40:203-223 © The Authors 2014